The time recorded in places within the same longitude.

A longitude is an imaginary line running from N to S which shows how far E or W a place is from the prime meridian.

Greenwich Meridian (0◦) longitude is the point of reference when calculating time.

Time is gained towards the E and lost towards the W.


  1. Suppose the time at GWM is 12 noon what is the local time at Jos 40◦E?

Time gained=40×4=160min=2 hours 40min

Local time at Jos is 12.00+2.40=14.40-1200=2.40pm.

  1. At Dar-es-Salaam 40◦E time is 12pm what is the time at Ecuador 40◦E?



Ecuador is behind in time =12.00-4=8 am.

If the places are on the same side subtract the degrees to get the difference and add or subtract from the reference time depending on which side the place is.

Calculation of Longitude

What is the longitude of place x whose local time is 8 am when local time at GWM is noon? Time difference =12.00-8=4 hours Degrees=4×15=60◦ Since x is behind in time its then 60◦W.

Standard Time and Zones

  • Standard time is time recorded by countries within the same time zone.
  • Standard time was come up with due to confusion resulting from time changing at every longitude.
  • The world has 24 time zones.

The International Date Line It’s the 180◦ longitude.

Effects of Crossing It

  • One gains time when he crosses it from W to E and has to adjust the clock ahead by 24 hours.
  • One loses time when he crosses it from E to W and has to adjust the clock backwards by 24 hours.

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